Candela Laser Corporation proposes to develop a diode laser system for the controlled interstitial illumination of tumors. The apparatus will be designed to utilize the combined effects of hyperthermia and other therapies to treat certain human malignancies. Prototype cylindrical tip interstitial optical fibers will be designed and evaluated for the distribution pattern of light delivery under realistic tissue conditions and in an in-vitro model. A feedback/control mechanism using implanted thermocouples will be developed to generate the desired hyperthermia temperature profile. The expected thermal distribution will be modelled and compared to in-vitro and in-vivo studies to test the effectiveness of the technique. The unique aspect is a low cost, compact, efficient, high power diode laser system using disposable treatment fibers and the fact that the system may be used in a stand-alone hyperthermia mode or combined not only with photodynamic therapy, but also other modalities such as chemo- or radiotherapy.